As a rule, shaft tools of this type are supplied with coolant/lubricant to a coolant/lubricant feeding point, for example in the form of a connection piece comprising a central coolant/lubricant supply duct. Frequently, connection to a supply part of a minimal-quantity-lubrication system takes place within a chuck.
Minimal-quantity-lubrication technology, i.e. minimal quantity or reduced quantity lubrication, is increasingly gaining in importance, in particular in process technology using cutting tools. The basic principle of this technology is to deliver a lubricant mist (a type of aerosol) comprising a minimum quantity of lubricant and considerable excess air at a consistency and quality that are as even as possible, to the working cutters. Any fluctuations in quality, for example fluctuations caused by cyclical or spontaneous demixing in the aerosol that is supplied at pressure, can result in unforeseeable tool breakage, and consequently, as a result of interruption of the production, to considerable damage.
A known arrangement of such an interface is for example shown in FIG. 1, to which reference is already made at this stage.
In FIG. 1 reference character 10 designates a tool holding fixture which at one end comprises a hollow-shaft cone 11 for accommodation in a tool system module or in a machine tool spindle, and which tool holding fixture at the other end comprises a cylindrical chuck part 13 for the actual accommodation of a tool 14, which in the example shown is an internally-cooled drilling tool. However, it should already be pointed out that the tool can also be some other rotary driven tool, such as for example a milling tool or a fine boring tool. In order to supply the internal ducts, designated 68, with coolant and lubricant, the tool holding fixture 10 comprises a threaded borehole 20 into which an insert 12 in the form of a locking screw has been turned. The thread 20 extends concentrically in relation to the axis A, from a bottom surface 25 of the recess 26 of the hollow-shaft cone 11 to the base area 28 of the cylindrical borehole 30 for accommodating the tool 14.
With its face pointing towards the tool the insert 12 rests against a face 32 of the tool 14, which face 32 points away from the tool tip (not shown). A central borehole 24 extends along the entire length of the insert 12, wherein the diameter of said central borehole 24 is approximately equal in size to the width of a diametrically extending slit 36 in the abutting face 32 of the tool 14. The diametrical slit 36 is aligned in such a way that it extends over the orifices of the two internal ducts 68.
For axial setting of the insert 12, a hexagon socket recess 40 is provided on the end facing away from the tool 14. This ensures that when the locking screw 12 is adjusted, the limit stop for the face 32 of the tool 14 is adjusted as well so that the axial position of the tool cutter (not shown) in relation to a face 42 of the tool holding fixture 10 can be fine-adjusted.
In order to clamp the tool, for example first the adjusting screw 12 is screwed into the threaded borehole 20 to a specified desired dimension. Thereafter the tool 14 is inserted into the cylindrical borehole 30 until said tool comes to rest against the locking screw 12, and then the clamping device, which in the example shown is an expansion chuck 44, is activated. The diagram shows that when coolant/lubricant is fed by way of the module of a clamping system, which module accommodates the hollow-shaft cone, even supply of the coolant channels 68 takes place in that the coolant/lubricant enters by way of the hexagon socket recess 40, from where it flows by way of the borehole 24 to the slit 36 that is aligned flush with said borehole 24, from which slit 36 said coolant/lubricant flows radially outward to the orifices of the internal ducts 68.
It has been shown that this design cannot reliably ensure that the desired cooling or lubricating effect occurs in a satisfactory manner, in particular if the tool is operated using so-called minimal quantity lubrication. It has been shown in detail that in the case of minimal quantity lubrication the lubricant mist that has to be conveyed through the internal ducts does not arrive at the cutter at the desired even consistency.
In order to provide improved control over these problems, various efforts have been made. For example, in patent specification DE 101 57 450 A1, a concept has been proposed by which stabilization of the mixture takes place in that several large-angle deflections of the flows or partial flows are avoided, as a result of which uncontrolled demixing of the lubricant mist is effectively countered.
However, this known solution requires a comparatively complex geometry of the engaging connecting surfaces between the tool shaft and the feed part, as a result of which tool costs increase, all the more so since the tools are frequently made from particularly high-strength materials that are more difficult to machine.